The 30-year-old Manu played for Tonga in the 2008 World Cup but now qualifies for England on residency, having moved to the United Kingdom in 2006 - initially to play for Castleford - and he was brought into McNamara's squad for a get-together in Liverpool this week.
McNamara's predecessor Tony Smith created much debate after handing Samoa-born prop Maurie Fa'asavalu a Great Britain debut in 2007.
"Willie Manu qualifies to play for England on residency and has made himself available," said an RFL spokesman.
You would thought that after picking Fasavalu the England team would have learned their lesson.
Bad news for the sport.
If this happens I wont be watching the England team.
It's just one player, one the other side what about the inclusion of Ben Jones-Bishop? Is that a joke? Keep calm and carry on dude.